Electronic position transducer for control members

ABSTRACT

A control circuit which eliminates the need for wiping contacts normally employed in conjunction with traction motors for use in operating vehicles. Forward or reverse operation of the traction motor (and hence the vehicle) is controlled by a plunger movable with the vehicle foot pedal. An oscillating circuit develops an output whose rate controls the speed of the traction motor. The output rate of the circuit, in turn, is controlled by any circuit having a storage member which alternatively either charges or discharges according to its electrical connection so as to cause the oscillating circuit to reach the final selected frequency in a gradual manner. A braking circuit is also provided for gradually braking the traction motor.

nited States Patent [1 1 Tateo et al.

ELECTRONIC POSITION TRANSDUCER FOR CONTROL MEMBERS Inventors: Vito Tateo, Milano; Guido Galli,

Bastiglia (Modena), both of Italy Assignee: Fabrica Italiana Magnet Marelli S.p.A., Milano, Italy Filed: Nov. 30, 1971 A pl. No.: 203,361

Foreign Application Priority Data Dec. 5, 1970 Italy 32715 A/70 US. Cl. 318/341, 318/466 Int. Cl. l-l02p 5/18 Field of.Search 318/139, 341, 415,

References Cited UNITED STATES PATENTS 7/1971 Thombs 318/341 X 10/1969 Warren et a1 318/341 X 3,027,516 3/1962 Brouwer 318/656 X Primary Examiner-Hemard A. Gilheany Assistant Examiner-W. E. Duncanson, Jr'. Attorney-Ostrolenk, Faber, Gerb & Soffen [57] ABSTRACT A control circuit which eliminates the need for wiping contacts normally employed in conjunction with traction motors for use in operating vehicles. Forward or reverse operation of the traction motor (and hence the vehicle) is controlled by a plunger movable with the vehicle foot pedal. An oscillating circuit develops an output whose rate controls the speed of the traction motor. The output rate of the circuit, in turn, is controlled by any circuit having a storage member which alternatively either charges or discharges according to its elec trical connection so as to cause the oscillating circuit to reach the final selected frequency in a gradual manner. A braking circuit is also provided for gradually braking the traction motor.

5 Claims, 1 Drawing Figure ELECTRONIC POSITION TRANSDUCER FOR CONTROL MEMBERS This invention relates to an electronic position transducer, that is a device capable of supplying an output signal which is linearly variable dependent on the position of a control member, particularly for traction motors of electric lifting trucks.

This type of known devices providing a direct current outlet normally comprise a variable resistor which is acted on by means of wiping contacts, driven by a control member, such as a pedal, hand lever or the like.

However, the use of wiping contacts causes deterioration of the contacts, which is the reason for continuous checks and replacements of the damaged parts.

Further, with known devices a gradual increase in the outlet signal cannot be assured from the rest condition of the control member, whatever is the operation rapidity of the member. As a result, should the signal be, for example, continuous and intended for controlling the regulation or setting of a direct current motor, there could occur at the initiation of operation a sudden starting of the motor and apparatus driven thereby, such as a vehicle, machine tool and the like.

The object of the present invention is to provide an electronic position transducer which is not subjected to wear of parts and is capable of supplying a gradual adjustable outlet signal, even when the control member is rapidly operated from the rest position to the full on position.

According to the invention, the transducer comprises .an oscillator supplying a differential transformer, the

secondary of which supplies the outlet signal and the plunger of which is synchronously moved by the con trol member.

In turn, the oscillator is controlled by a modulator gradually adjusting the rated input by acting on the bias of a semiconductor device supplying the differential transformer.

According to a preferred embodiment, the oscillator is an LC oscillator and its coil is coincident with the primary of the differential transformer, while the modulator controls the oscillator by means of a semiconductor device. This device is connected in a discharge circuit for a capacitor which, in turn, is charged through a unidirectional line comprising at least one switch operated by the corresponding control member, and a resistive divider. This divider sets the capacitor charge level and thus the discharge time during which the modulator controls the oscillator rated input.

Should the signal be used for controlling the setting of a direct current motor, the direct current signal is provided by means of a converter supplied from the secondary of the differential transformer.

Further features and advantages of the invention will become more apparent from the following description with reference to the figure which, by mere way of nonlimiting example, relates to a position transducer for an electric lifting truck.

The circuit shows the position for the several parts at rest conditions.

According to the invention, said circuit comprises, in combination, an oscillator OS, a converter CO having its output U connected to the setting system for the direct current motor (not shown), a differential transformer TD coupling the oscillator to a modulator MO,

the latter controlling the oscillator at the initial operating step. I

l, and I designate two switches connected in the modulator supply circuit and controlled by the truck pedals P, and P respectively. One pedal is for forward movement and the other pedal is for reverse movement of the vehicle. The electrical connections to the motor for controlling the movement direction are not shown, neither is shown the mechanical connection between the pedals, this connection being designed so that only one pedal at a time can be operated. Each of the pedals are also mechanically connected, as symbolically shown by broken lines L, and L to the plunger N of the differential transformer TD, so as to cause a synchronous movement thereof. Of course, this plunger is alternately controlled by pedal P, or P At movement start, each pedal will open the corresponding switch.

At rest condition (pedals not operated), the plunger connects to the same extent the two opposite windings of secondary S to the primary winding P of the transformer TD. This is a condition to which at input E to converter CO always corresponds to zero voltage, since the voltages in the two windings of secondary S are of equal magnitude and opposite polarity. Oscillator OS is of a known type (Colpitts oscillator) and substantially comprises a transistor T,, a bias voltage divider R,, R, which by its intermediate point A is connected to the base of transistor T,, the collector and emitter resistors R R,, and the reaction network comprising capacitors C, and C, and coil P, this network being connected to the input of transistor T, by means of a capacitor C The oscillator is completed by a network C,-R connecting the resistor R, to ground. Voltage divider R,, R, is connected through a switch I to the supply source +B. In this oscillator, which is an LC type of oscillator, the coil P is also serves as the primary of the differential transformer TD.

Modulator MO comprises a transistor T, which is connected ina discharge circuit for a capacitor C, including a resistor R,,. In turn, this capacitor C is connected to +B through a line comprising the switches l 1,, I,, a resistor R, and a diode D. Variable resistor R and resistor R, form a resistive divider for setting the level for the capacitor charge voltage. The level becomes higher as the value of resistor R, is increased.

The collector of transistor T, is connected to point A of divider R,, R, so as to act on the bias of transistor T,. The operation of the circuit is as follows:

Closure of switch I Pedals P, and P, being at a rest condition, as soon as switch I is closed, capacitor C is charged through the network comprising switches I, I,, I resistor R diode D, capacitor C, and ground. When the changing of C, is completed T, is saturated. Under these conditions and due to the collector saturation current, the voltage of point A takes a very low value, which is not sufficient to turn on transistor T, which, therefore, remains cut off. Thus, for the whole period of time the above capacitor C is charged (switches l, and I, closed), the oscillator OS is inoperative.

Next operation of a pedal By pressing down one of the pedals (P, or P according to the movement direction being involved, the opening of the corresponding switch (I, or I,) is provided and at the same time plunger N of the differential transformer TD is moved. Thus, the supply to capacitor C, is cut off, while switch I, which is kept at a closed condition, continues to retain the connection between the divider R R and supply +B.

Under these conditions the discharge of capacitor C, will commence through resistor R and transistor T the discharge time of the capacitor C depending on the level of its charge voltage set by the variable resistor R During this time, the voltage at point A will pass from the very low level for the saturation condition of transistor T to a higher level sufficient to bias the transistor T and defined by divider R R when the discharge is completed and the collector current of transistor T is zero. Accordingly, during this time the bias of the base of transistor T gradually increases, assuring at the operation beginning the gradually rating for the oscillator. This means that at starting, whatever is the rapidity in operation and then position taken by the pedal, and hence the coupling extent between primary P and secondary S, a gradually increasing voltage is always applied to the input E of converter CO, reaching the rating value corresponding to to the pedal position at the end of discharge of capacitor C Obviously, by adjusting resistor R the discharge time for capacitor C can be varied and accordingly the bias voltage pattern on the base of transistor T can be varied and, finally that for the input and output voltage of the converter CO prior to the circuit rated operation.

The starting step ends with the discharge of capacitor C and the modulator MO no longer exerts any control on the oscillator OS which will operate at a rated condition with a constant continuous bias provided by the divider R R Under these conditions the output voltage of converter CO will depend on the pedal position according to the truck speed requirements.

The invention has been described herein by mere way of example with reference to a particular application for the transducer, it being however apparent that the circuit is liable to modifications in accordance with the particular requirements, without departing for this from the scope of the invention.

Thus, only one switch could be provided instead of the two switches l and above mentioned, as well as the control member could be different from the pedal and automatically operated, rather than being operated by the operator.

Also the oscillator and the supply system for the differential transformer could be different from those shown herein.

Further, by slight modifications the modulator could be such as to act on the oscillator during the capacitor charging rather than during the discharging stage of said capacitor.

With the term converter as herein used it should be meant any circuit capable of receiving at its input an alternate current voltage and providing a direct current voltage at its output. This circuit could be simply a rectifier filter. It could also be dispensed with in case an alternate current signal is desired at the output of the differential transformer.

Of course, this would depend on the particular application of the circuit.

Where the device is used for adjusting the supply of a direct current traction motor, particularly a motor for lifting trucks, and an electrical braking of the motor is desired, the above shown device is completed by the circuit AS applied to the terminals 1 and 2 of capacitor On braking step, this circuit is for stabilizing the base voltage in the transistor T of oscillator OS to a predetermined reduced rate, so that the voltage across the primary winding P of the differential transformer TD is lower and, accordingly, the U voltage at the output of converter CO, forming the reference signal for the motor control system, is lower with the control member position being unchanged. Under these conditions, a gradual braking of the motor is ensured.

The circuit AS accomplishes this object by setting at a given rate the discharge voltage of capacitor C at the motor braking step. As shown in the diagram, this circuit comprises in a series connection a stabilized power supply 3, a diode 4 and a reed switch 5. The predetermined fixed voltage, power supply 3 can be of any known design. The coil 6 of switch 5 is applied across the motor armature and is energized only by the braking current through a reverse diode, not shown.

Upon energization of coil 6, contact 7 is closed and capacitor C is connected to circuit AS. Under these conditions, during the discharge of capacitor C through resistor R and transistor T the voltage across terminals 1 and 2 is reduced to the voltage rate set by the power supply 3, whereupon it remains stabilized along with the voltage at point A, which is the base of transistor T,

On braking release, coil 6 is de-energized, contact 7 is opened and the capacitor starts to discharge again, correspondingly causing an increase in the voltage at point A to the rate set by the divider R R and then the device resumes its operation as above described.

What is claimed is:

1. An electronic position transducer for a movable drive member comprising a power source;

an oscillator coupled to said power source;

a differential transformer coupled to the output of said oscillator;

said transformer having a removable core;

linking means coupled between said movable core and said drive member to position said core in relationship to the positioning of said drive member; switch means coupled to said power source; modulator means having a control network coupled to said switch means and a semiconductor device coupled to said control network;

said control network having storage means charged by said power source; the output of said semiconductor being coupled to the input of said oscillator; said switch means being normally closed to charge said storage means when said drive member is in the rest position and being operated by said drive member to the open position to enable said storage means to discharge gradually when said drive member is operated; said control network being adapted to deenergize said oscillator when said drive member is in the rest position and being adapted to gradually energize said oscillator and thereby prevent the output of said differential transformer from changing abruptly. 2. The electronic position transducer of claim 1, further comprising a voltage divider coupled to said switch means;

.a diode coupled between said divider and said control network, said semiconductor device comprising a transistor, for developing a bias for said oscillator which is inversely proportional to the conduction state of said transistor.

3. An electronic position transducer as claimed in claim 1, as used for controlling the operation of a motor-vehicle D.C. traction motor, wherein said drive member is the running pedal of said vehicle and the output voltage from the differential transformer is coupled to a rectifier means for controlling the direct supply circuit of the motor.

4. An electronic position transducer as claimed in output winding forming part of said oscillator means. 

1. An electronic position transducer for a movable drive member comprising a power source; an oscillator coupled to said power source; a differential transformer coupled to the output of said oscillator; said transformer having a removable core; linking means coupled between said movable core and said drive member to position said core in relationship to the positioning of said drive member; switch means coupled to said power source; modulator means having a control network coupled to said switch means and a semiconductor device coupled to said control network; said control network having storage means charged by said power source; the output of said semiconductor being coupled to the input of said oscillator; said switch means being normally closed to charge said storage means when said drive member is in the rest position and being operated by said drive member to the open position to enable said storage means to discharge gradually when said drive member is operated; said control network being adapted to deenergize said oscillator when said drive member is in the rest position and being adapted to gradually energize said oscillator and thereby prevent the output of said differential transformer from changing abruptly.
 2. The electronic position transducer of claim 1, further comprising a voltage divider coupled to said switch means; a diode coupled between said divider and said control network, said semiconductor device comprising a transistor, for developing a bias for said oscillator which is inversely proportional to the conduction state of said transistor.
 3. An electronic position transducer as claimed in claim 1, as used for controlling the operation of a motor-vehicle D.C. traction motor, wherein said drive member is the running pedal of said vehicle and the output voltage from the differential transformer is coupled to a rectifier means for controlling the direct supply circuit of the motor.
 4. An electronic position tranSducer as claimed in claim 3 wherein said power source further comprises a voltage stabilizer having a stabilized reduced voltage supply, normally open means coupling said stabilizer to said control network; relay means energized by the motor braking current to limit the output of said oscillator for controlling the reverse supply circuit for the motor, said circuit being connected upon pedal operation.
 5. The transducer of claim 1 wherein said differential transformer comprises input and output windings; said output winding forming part of said oscillator means. 